Search

Iodine intersects with the marine biogeochemical cycles of several major elements and can influence air quality through reactions with tropospheric ozone. Iodine is also an element of interest in paleoclimatology, whereby iodine-to-calcium ratios in marine carbonates are widely used as a proxy for past ocean redox state. While inorganic iodine in seawater is found predominantly in its reduced and oxidized anionic forms, iodide (I−) and iodate (IO3−), the rates, mechanisms and intermediate species by which iodine cycles between these inorganic pools are poorly understood. Here, we address these issues by characterizing the speciation, composition and cycling of iodine in the upper 1,000 m of the water column at Station ALOHA in the subtropical North Pacific Ocean. We first obtained high-precision profiles of iodine speciation using isotope dilution and anion exchange chromatography, with measurements performed using inductively coupled plasma mass spectrometry (ICP-MS). These profiles indicate an apparent iodine deficit in surface waters approaching 8% of the predicted total, which we ascribe partly to the existence of dissolved organic iodine that is not resolved during chromatography. To test this, we passed large volumes of seawater through solid phase extraction columns and analyzed the eluent using high-performance liquid chromatography ICP-MS. These analyses reveal a significant pool of dissolved organic iodine in open ocean seawater, the concentration and complexity of which diminish with increasing water depth. Finally, we analyzed the rates of IO3− formation using shipboard incubations of surface seawater amended with 129I−. These experiments suggest that intermediate iodine species oxidize to IO3− much faster than I− does, and that rates of IO3− formation are dependent on the presence of particles, but not light levels. Our study documents the dynamics of iodine cycling in the subtropical ocean, highlighting the critical role of intermediates in mediating redox transformations between the major inorganic iodine species. [ABSTRACT FROM AUTHOR]

Fluids mediate the transport of subducted slab material and play a crucial role in the generation of arc magmas. However, the source of subduction-derived fluids remains debated. The Kamchatka arc is an ideal subduction zone to identify the source of fluids because the arc magmas are comparably mafic, their source appears to be essentially free of subducted sediment-derived components, and subducted Hawaii-Emperor Seamount Chain (HESC) is thought to contribute a substantial fluid flux to the Kamchatka magmas. Here we show that Tl isotope ratios are unique tracers of HESC contribution to Kamchatka arc magma sources. In conjunction with trace element ratios and literature data, we trace the progressive dehydration and melting of subducted HESC across the Kamchatka arc. In succession, serpentine (<100 km depth), lawsonite (100–250 km depth) and phengite (>250 km depth) break down and produce fluids that contribute to arc magmatism at the Eastern Volcanic Front (EVF), Central Kamchatka Depression (CKD), and Sredinny Ridge (SR), respectively. However, given the Tl-poor nature of serpentine and lawsonite fluids, simultaneous melting of subducted HESC is required to explain the HESC-like Tl isotope signatures observed in EVF and CKD lavas. In the absence of eclogitic crust melting processes in this region of the Kamchatka arc, we propose that progressive dehydration and melting of a HESC-dominated mélange offers the most compelling interpretation of the combined isotope and trace element data. Fluids released from progressive breakdown of minerals at increasing pressure within a mélange may explain the trace element systematics and stable thallium isotope data of the Kamchatka arc lavas from volcanic front to back arc. [ABSTRACT FROM AUTHOR]

Thallium (Tl) isotope ratios are an emerging tool that can be used to trace crustal recycling processes in arc lavas and ocean island basalts (OIBs). Thallium is a highly volatile metal that is enriched in volcanic fumaroles, but it is unknown whether degassing of Tl from subaerial lavas has a significant effect on their residual Tl isotope compositions. Here, we present Tl isotope and concentration data from degassing experiments that are best explained by Rayleigh kinetic isotope fractionation during Tl loss. Our data closely follow predicted isotope fractionation models in which TlCl is the primary degassed species and where Tl loss is controlled by diffusion and natural convection, consistent with the slow gas advection velocity utilized during our experiments. We calculate that degassing into air should be associated with a net Tl isotope fractionation factor of αnet = 0.99969 for diffusion and natural gas convection (low gas velocities) and αnet = 0.99955 for diffusion and forced gas convection (high gas velocities). We also show that lavas from three volcanoes in the Kamchatka arc exhibit Tl isotope and concentration patterns that plot in between the two different gas convection regimes, implying that degassing played an important role in controlling the observed Tl isotope compositions in these three volcanoes. Literature inspection of Tl isotope data for subaerial lavas reveals that the majority of these appear only minorly affected by degassing, although a few samples from both OIBs and arc volcanoes can be identified that likely experienced some Tl degassing. Plain Language Summary: Volcanic degassing is an important process for understanding emissions to the atmosphere of greenhouse gasses and toxic metals. Thallium (Tl) is a toxic metal that is highly volatile, which in recent years has been developed as a stable isotope system that can be applied to understand the transfer of material from the Earth surface to the deep mantle via measurements of volcanic lavas. However, degassing of Tl from volcanic lavas could potentially alter the isotope ratio of the residual lava and, thus, render applications of Tl isotopes in lavas difficult to relate to deep Earth material transfer. Here, we perform the first study of Tl isotopes in degassing experiments. These reveal that Tl isotope ratios progressively become enriched in the heavy isotope with loss of Tl. We also show that natural lavas from Kamchatka follow similar Tl depletion and isotope enrichment patterns as our experiments, which for the first time demonstrates that degassing in nature is associated with diffusion‐controlled loss of the light Tl isotope. Key Points: Degassing of Tl from experimental melts are associated with kinetic isotope fractionation limited by diffusion in the gas phaseBasaltic lavas from Kamchatka follow the same Tl depletion‐isotope fractionation pattern as experimental chargesThe majority of literature Tl isotope data for volcanic lavas reveal only limited effects from degassing [ABSTRACT FROM AUTHOR]

Carbonatite volcanism remains poorly understood compared to silicic volcanism due to the scarcity of carbonatite volcanoes worldwide and because volcanic H2O and CO2—major components in carbonatite volcanic systems—are not well preserved in the rock record. To further our understanding of carbonatite genesis, we utilize the non‐traditional thallium (Tl) isotope system in Khanneshin carbonatites in Afghanistan. These carbonatites contain 250–30,000 ng/g Tl and have ε205Tl values (−4.6 to +4.6) that span much of the terrestrial igneous range. We observe that δ18OVSMOW (+8.6‰ to +23.5‰) correlates positively with δ13CVPDB (−4.6‰ to +3.5‰) and ε205Tl up to δ18O = 15‰. Rayleigh fractionation of calcite from an immiscible CO2‐H2O fluid with a mantle‐like starting composition can explain the δ18O and δ13C—but not ε205Tl—trends. Biotite fractionates Tl isotopes in other magmatic settings, so we hypothesize that a Tl‐rich hydrous brine caused potassic metasomatism (i.e., biotite fenitization) of wall rock that increased the ε205Tl of the residual magma‐fluid reservoir. Our results imply that, in carbonatitic volcanic systems, simultaneous igneous differentiation and potassic metasomatism increase ε205Tl, δ18O, δ13C, and light rare earth element concentrations in residual fluids. Our fractionation models suggest that the Tl isotopic compositions of the primary magmas were among the isotopically lightest (less than or equal to ε205Tl = −4.6) material derived from the mantle for which Tl isotopic constraints exist. If so, the ultimate source of Tl in Khanneshin lavas—and perhaps carbonatites elsewhere—may be recycled ocean crust. Plain Language Summary: Most volcanoes on Earth are silica‐rich. Rare volcanoes that are composed of mostly carbonate minerals (referred to as carbonatite volcanoes) are not as well understood, but provide clues about carbon fluxes into and out of the mantle. To further our understanding of carbonatite genesis, we measured the thallium, oxygen, and carbon isotopes in rocks from a carbonatite volcano in Afghanistan. We discovered systematic variations in all three isotope systems caused by the massive release of carbon dioxide‐ and water‐rich fluids from the magmas prior to eruption. Interaction between these fluids and the surrounding rock—which we argue is fundamental to carbonatite genesis—appears to be largely responsible for magma evolution. As the first study of thallium isotopes in carbonatites, our results also have implications for the origins of carbonatite magmas: we infer that the magmas initially had thallium isotope compositions most similar to ocean crust, which implies that seafloor thallium cycles deep into the mantle and returns to the surface in carbonatitic magmas. Key Points: Thallium isotopes fractionate in carbonatite volcanic systemsThallium in carbonatites may derive from recycled ocean crustBrines cause potassic metasomatism during ascent and eruption of carbonatite magmas [ABSTRACT FROM AUTHOR]

The Nd isotope composition of seawater has been used to reconstruct past changes in the contribution of different water masses to the deep ocean. In the absence of contrary information, the Nd isotope compositions of endmember water masses are usually assumed constant during the Quaternary. Here we show that the Nd isotope composition of North Atlantic Deep Water (NADW), a major component of the global overturning ocean circulation, was significantly more radiogenic than modern during the Last Glacial Maximum (LGM), and shifted towards modern values during the deglaciation. We propose that weathering contributions of unradiogenic Nd modulated by the North American Ice Sheet dominated the evolution of the NADW Nd isotope endmember. If water mass mixing dominated the distribution of deep glacial Atlantic Nd isotopes, our results would imply a larger fraction of NADW in the deep Atlantic during the LGM and deglaciation than reconstructed with a constant northern endmember. The Nd isotope composition of seawater has been used to reconstruct past changes in the various contributions of different water masses to the deep ocean, with the isotope signatures of endmember water masses generally assumed to have been stable during the Quaternary. Here, the authors show that deep water produced in the North Atlantic had a significantly more radiogenic Nd signature during the Last Glacial Maximum compared to today. [ABSTRACT FROM AUTHOR]

New bulk sediment Sr and Nd isotope data, coupled with U–Pb dating of detrital zircon grains from sediment cored by the International Ocean Discovery Program in the Arabian Sea, allow the reconstruction of erosion in the Indus catchment since ∼17 Ma. Increasing εNd values from 17 to 9.5 Ma imply relatively more erosion from the Karakoram and Kohistan, likely linked to slip on the Karakoram Fault and compression in the southern and eastern Karakoram. After a period of relative stability from 9.5 to 5.7 Ma, there is a long-term decrease in εNd values that corresponds with increasing relative abundance of >300 Ma zircon grains that are most common in Himalayan bedrocks. The continuous presence of abundant Himalayan zircons precludes large-scale drainage capture as the cause of decreasing εNd values in the submarine fan. Although the initial increase in Lesser Himalaya-derived 1500–2300 Ma zircons after 8.3 Ma is consistent with earlier records from the foreland basin, the much greater rise after 1.9 Ma has not previously been recognized and suggests that widespread unroofing of the Crystalline Lesser Himalaya and to a lesser extent Nanga Parbat did not occur until after 1.9 Ma. Because regional erosion increased in the Pleistocene compared to the Pliocene, the relative increase in erosion from the Lesser Himalaya does not reflect slowing erosion in the Karakoram and Greater Himalaya. No simple links can be made between erosion and the development of the South Asian Monsoon, implying a largely tectonic control on Lesser Himalayan unroofing. [ABSTRACT FROM AUTHOR]

In 2015 a geothermal exploration well was drilled on the island of Tutuila, American Samoa. The sample suite from the drill core provides 645 m of volcanic stratigraphy from a Samoan volcano, spanning 1.45 million years of volcanic history. In the Tutuila drill core, shield lavas with an EM2 (enriched mantle 2) signature are observed at depth, spanning 1.46 to 1.44 Ma. These are overlain by younger (1.35 to 1.17 Ma) shield lavas with a primordial "common" (focus zone) component interlayered with lavas that sample a depleted mantle component. Following ~1.15 Myr of volcanic quiescence, rejuvenated volcanism initiated at 24.3 ka and samples an EM1 (enriched mantle 1) component. The timing of the initiation of rejuvenated volcanism on Tutuila suggests that rejuvenated volcanism may be tectonically driven, as Samoan hotspot volcanoes approach the northern terminus of the Tonga Trench. This is consistent with a model where the timing of rejuvenated volcanism at Tutuila and at other Samoan volcanoes relates to their distance from the Tonga Trench. Notably, the Samoan rejuvenated lavas have EM1 isotopic compositions distinct from shield lavas that are geochemically similar to "petit spot" lavas erupted outboard of the Japan Trench and late stage lavas erupted at Christmas Island located outboard of the Sunda Trench. Therefore, like the Samoan rejuvenated lavas, petit spot volcanism in general appears to be related to tectonic uplift outboard of subduction zones, and existing geochemical data suggest that petit spots share similar EM1 isotopic signatures. Key Points: Within the 645‐m Tutuila drill core we find isotopically heterogeneous lavas as well as several abrupt temporal and geochemical boundariesThe proximity of Samoan volcanoes to the Tonga Trench and geochronology are consistent with a tectonic influence on rejuvenated volcanismThe tectonic setting and isotopic signatures of the Samoan rejuvenated lavas link them to "petit spots" outboard of the Japan Trench [ABSTRACT FROM AUTHOR]

New bulk sediment Sr and Nd isotope data, coupled with U-Pb dating of detrital zircon grains from sediment cored by International Ocean Discovery Program in the Arabian Sea, allow reconstruction of erosion in the Indus catchment since ~17Ma. Increasing εNd values from 17 to 9.5Ma imply relatively more erosion from the Karakoram/Kohistan, likely linked to slip on the Karakoram Fault and compression in the Southern and Eastern Karakoram. After a period of relative stability from 9.5 to 5.7Ma there is a long-term decrease in εNd values that correlates with increasing relative abundance of >300Ma zircon grains that are most common in Himalayan bedrocks, precluding large-scale drainage capture as the cause of decreasing εNd values in the submarine fan. Although the initial increase in Lesser Himalaya-derived 1500-2300Ma zircons after 8.3Ma is consistent with earlier records from the foreland basin the much greater rise after 1.9Ma, has not previously been recognized and suggests that widespread unroofing of the Crystalline Lesser Himalaya and to a lesser extent Nanga Parbat did not occur until after 1.9Ma. No simple links can be made between erosion and the development of the South Asian Monsoon, implying a largely tectonic control to Lesser Himalayan unroofing. [ABSTRACT FROM AUTHOR]

The Ayeyawady delta is the last Asian megadelta whose evolution has remained essentially unexplored so far. Unlike most other deltas across the world, the Ayeyawady has not yet been affected by dam construction, providing a unique view on largely natural deltaic processes benefiting from abundant sediment loads affected by tectonics and monsoon hydroclimate. To alleviate the information gap and provide a baseline for future work, here we provide a first model for the Holocene development of this megadelta based on drill core sediments collected in 2016 and 2017, dated with radiocarbon and optically stimulated luminescence, together with a reevaluation of published maps, charts and scientific literature. Altogether, these data indicate that Ayeyawady is a mud-dominated delta with tidal and wave influences. The sediment-rich Ayeyawady River built meander belt alluvial ridges with avulsive characters. A more advanced coast in the western half of the delta (i.e., the Pathein lobe) was probably favored by the more western location of the early course of the river. Radiogenic isotopic fingerprinting of the sediment suggests that the Pathein lobe coast does not receive significant sediment from neighboring rivers. However, the eastern region of the delta (i.e., Yangon lobe) is offset inland and extends east into the mudflats of the Sittaung estuary. Wave-built beach ridge construction during the late Holocene, similar to several other deltas across the Indian monsoon domain, suggests a common climatic control on monsoonal delta morphodynamics through variability in discharge, changes in wave climate or both. Correlation of the delta morphological and stratigraphic architecture information on land with the shelf bathymetry, as well as its tectonic, sedimentary and hydrodynamic characteristics, provides insight on the peculiar growth style of the Ayeyawady delta. The offset between the western Pathein lobe and the eastern deltaic coast appears to be driven by tectonic-hydrodynamic feedbacks as the extensionally lowered shelf block of the Gulf of Mottama amplifies tidal currents relative to the western part of the shelf. This situation probably activates a perennial shear front between the two regions that acts as a leaky energy fence. Just as importantly, the strong currents in the Gulf of Mottama act as an offshore-directed tidal pump that helps build the deep mid-shelf Mottama clinoform with mixed sediments from the Ayeyawady, Sittaung and Thanlwin rivers. The highly energetic tidal, wind and wave regime of the northern Andaman Sea thus exports most sediment offshore despite the large load of the Ayeyawady River. [ABSTRACT FROM AUTHOR]

Alkaline magmatism associated with the West Antarctic rift system in the NW Ross Sea (NWRS) includes a north-south chain of shield volcano complexes extending 260km along the coast of Northern Victoria Land (NVL), numerous small volcanic seamounts located on the continental shelf and hundreds more within an ~35 000km2 area of the oceanic Adare Basin. New 40Ar/39Ar age dating and geochemistry confirm that the seamounts are of Pliocene-Pleistocene age and petrogenetically akin to the mostly middle to late Miocene volcanism on the continent, as well as to a much broader region of diffuse alkaline volcanism that encompasses areas of West Antarctica, Zealandia and eastern Australia. All of these continental regions were contiguous prior to the late-stage breakup of Gondwana at ~100 Ma, suggesting that the magmatism is interrelated, yet the mantle source and cause of melting remain controversial. The NWRS provides a rare opportunity to study cogenetic volcanism across the transition from continent to ocean and consequently offers a unique perspective from which to evaluate mantle processes and the roles of lithospheric and sublithospheric sources for mafic alkaline magmas. Mafic alkaline magmas with >6wt % MgO (alkali basalt, basanite, hawaiite, and tephrite) erupted across the transition from continent to ocean in the NWRS show a remarkable systematic increase in silica-undersaturation, P2O5, Sr, Zr, Nb and light rare earth element (LREE) concentrations, as well as LREE/HREE (heavy REE) and Nb/Y ratios. Radiogenic isotopes also vary, with Nd and Pb isotopic compositions increasing and Sr isotopic compositions decreasing oceanward. These variations cannot be explained by shallow-level crustal contamination or by changes in the degree of mantle partial melting, but are considered to be a function of the thickness and age of the mantle lithosphere. We propose that the isotopic signature of the most silica-undersaturated and incompatible element enriched basalts best represent the composition of the sub-lithospheric magma source with low 87Sr/86Sr (≥0≥7030) and δ18O olivine (≥5·0), and high 143Nd/144Nd (~0·5130) and 206Pb/204Pb (≤20). The isotopic 'endmember' signature of the sub-lithospheric source is derived from recycled subducted materials and was transferred to the lithospheric mantle by small-degree melts (carbonate-rich silicate liquids) to form amphibole-rich metasomes. Later melting of the metasomes produced silica-undersaturated liquids that reacted with the surrounding peridotite. This reaction occurred to a greater extent as the melt traversed through thicker and older lithosphere continentward. Ancient and/or more recent (~550-100 Ma) subduction along the Pan-Pacific margin of Gondwana supplied the recycled subduction-related material to the asthenosphere. Melting and carbonate metasomatism were triggered during major episodes of extension beginning in the Late Cretaceous, but alkaline magmatism was very limited in its extent. A significant delay of ~30 to 20 Myr between extension and magmatism was probably controlled by conductive heating and the rate of thermal migration at the base of the lithosphere. Heating was facilitated by regional mantle upwelling, possibly driven by slab detachment and sinking into the lower mantle and/or by edge-driven mantle flow established at the boundary between the thinned lithosphere of the West Antarctic rift and the thick East Antarctic craton. [ABSTRACT FROM AUTHOR]

Soil erosion plays a crucial role in transferring sediment and carbon from land to sea, yet little is known about the rhythm and rates of soil erosion prior to the most recent few centuries. Here we reconstruct a Holocene erosional history from central India, as integrated by the Godavari River in a sediment core from the Bay of Bengal. We quantify terrigenous fluxes, fingerprint sources for the lithogenic fraction and assess the age of the exported terrigenous carbon. Taken together, our data show that the monsoon decline in the late Holocene significantly increased soil erosion and the age of exported organic carbon. This acceleration of natural erosion was later exacerbated by the Neolithic adoption and Iron Age extensification of agriculture on the Deccan Plateau. Despite a constantly elevated sea level since the middle Holocene, this erosion acceleration led to a rapid growth of the continental margin. We conclude that in monsoon conditions aridity boosts rather than suppresses sediment and carbon export, acting as a monsoon erosional pump modulated by land cover conditions. [ABSTRACT FROM AUTHOR]

During the Bølling-Allerød warm period of the last deglaciation, about 14 kyr ago, there was a strong and pervasive spike in primary productivity in the North Pacific Ocean. It has been suggested that this productivity event was caused by an influx of the micronutrient iron from surrounding continental shelves as they were flooded by sea-level rise. Here we test this hypothesis by comparing numerous proxies of productivity with iron flux and provenance measured from a core from the subarctic Pacific Ocean. We find no evidence for an abrupt deglacial pulse of iron from any source at the time of peak productivity. Instead, we argue that the deglacial productivity peak was caused by two stepwise events. First, deep convection during early deglaciation increased nutrient supply to the surface but also increased the depth of the mixed layer, which pushed surface production deeper in the water column and induced light limitation. A subsequent input of meltwater from northern American ice sheets then stratified the water column, which relieved light limitation while leaving the surface waters enriched in nutrients. We conclude that iron plays, at most, a secondary role in controlling productivity during the glacial and deglacial periods in the subarctic Pacific Ocean. [ABSTRACT FROM AUTHOR]

We developed a new method for the determination of Ac in geological samples. The method uses extraction chromatographic techniques and alpha-spectrometry and is applicable for a range of natural matrices. Here we report on the procedure and results of the analysis of water (fresh and seawater) and rock samples. Water samples were acidified and rock samples underwent total dissolution via acid leaching. A DGA ( N, N, N′, N′-tetra- n-octyldiglycolamide) extraction chromatographic column was used for the separation of actinium. The actinium fraction was prepared for alpha spectrometric measurement via cerium fluoride micro-precipitation. Recoveries of actinium in water samples were 80 ± 8 % (number of analyses n = 14) and in rock samples 70 ± 12 % ( n = 30). The minimum detectable activities (MDA) were 0.017-0.5 Bq kg for both matrices. Rock sample Ac activities ranged from 0.17 to 8.3 Bq kg and water sample activities ranged from below MDA values to 14 Bq kgof Ac. From the analysis of several standard rock and water samples with the method we found very good agreement between our results and certified values. [ABSTRACT FROM AUTHOR]

Testosterone administration increases hemoglobin levels and has been used to treat anemia of chronic disease. Erythrocytosis is the most frequent adverse event associated with testosterone therapy of hypogonadal men, especially older men. However, the mechanisms by which testosterone increases hemoglobin remain unknown. Testosterone administration in male and female mice was associated with a greater increase in hemoglobin and hematocrit, reticulocyte count, reticulocyte hemoglobin concentration, and serum iron and transferrin saturation than placebo. Testosterone downregulated hepatic hepcidin m RNA expression, upregulated renal erythropoietin m RNA expression, and increased erythropoietin levels. Testosterone-induced suppression of hepcidin expression was independent of its effects on erythropoietin or hypoxia-sensing mechanisms. Transgenic mice with liver-specific constitutive hepcidin over-expression failed to exhibit the expected increase in hemoglobin in response to testosterone administration. Testosterone upregulated splenic ferroportin expression and reduced iron retention in spleen. After intravenous administration of transferrin-bound 58Fe, the amount of 58Fe incorporated into red blood cells was significantly greater in testosterone-treated mice than in placebo-treated mice. Serum from testosterone-treated mice stimulated hemoglobin synthesis in K562 erythroleukemia cells more than that from vehicle-treated mice. Testosterone administration promoted the association of androgen receptor ( AR) with Smad1 and Smad4 to reduce their binding to bone morphogenetic protein ( BMP)-response elements in hepcidin promoter in the liver. Ectopic expression of AR in hepatocytes suppressed hepcidin transcription; this effect was blocked dose-dependently by AR antagonist flutamide. Testosterone did not affect hepcidin m RNA stability. In conclusion, testosterone inhibits hepcidin transcription through its interaction with BMP/ Smad signaling. Testosterone administration is associated with increased iron incorporation into red blood cells. [ABSTRACT FROM AUTHOR]

Analyses of lead (Pb) isotopes have been performed in terrestrial and fresh water environments to estimate historical uses of leaded fuel, but so far this method has not been employed in studies of world-wide marine surface sediments. We analyzed Pb and its isotopes in 23 surface sediments from four continents collected during the Galathea 3 expedition in 2006–2007. To enhance the anthropogenic signal, a partial digestion using nitric acid was performed. The concentrations of Pb, Th, U and Al were determined with an ICP-Quadrupole MS, and Pb-isotope ratios with an ICP-multi-collector MS. The samples could be divided into three groups: Harbor areas in larger cities with concentrations of 150 to 265 mg kg−1 dry weight, smaller towns with concentrations between 20 and 40 mg kg−1 dry weight, and remotely located sites with concentrations below 15 mg kg−1 dry weight. Pb-isotope ratios were compared to literature values for gasoline and local or geological background values, and the contribution of leaded-gasoline to total concentrations was calculated for contaminated sites using both a one-dimensional and a novel two-dimensional (vector) method. The North American sites had Pb-isotope ratios corresponding to the US leaded gasoline, with 24–88% of the Pb from leaded gasoline. Samples from Oceania showed Pb-isotope ratios corresponding to Australian gasoline, with 60% attributed to leaded gasoline in Sydney and 21% in Christchurch. Outside Cape Town, 15 to 46% of Pb in sediments was from leaded gasoline. [ABSTRACT FROM AUTHOR]

A comparatively simple, rapid, low-blank, high-precision and reproducible technique for Nd isotope analysis (143Nd/144Nd) of trace amounts (1–5 ng) of Nd by multi-collector inductively coupled plasma mass spectrometry (MC-ICP-MS) was developed and is reported here. The technique utilizes a combination of a high-sensitivity desolvator (Aridus II or APEX-IR) and high-efficiency Jet-sample/X-skimmer cones, together with high-yield pre-concentration and column chemistry, to achieve optimal conditions for Nd isotope determination in natural materials with a variety of Nd-depleted matrices. This new method was validated by analyzing a series of international reference materials (RMs), which span a wide range of the Nd isotopic composition and cover different sample matrices in order to provide a useful benchmark for future studies. The long-term precision of 143Nd/144Nd (±0.000016, 2SD) for a sample size of ca. 1.25 ng Nd is a factor of 5 better than the existing high-sensitivity MC-ICP-MS methods using ＜2 ng of Nd and is comparable to the best TIMS methods. Replicate analyses of the RMs, including JNdi-1 (0.512116 ± 0.000016, 2SD), AGV-1 (0.512794 ± 0.000013, 2SD), BHVO-1 (0.512992 ± 0.000015, 2SD), Nod-P-1 (0.512430 ± 0.000015, 2SD) and two sets of synthetic solutions for seawater and calcium carbonate matrices, are in excellent agreement with the published values, demonstrating the robustness of the present protocol for natural samples with different matrices. A depth profile of the seawater Nd isotopes near the Bermuda Atlantic Time-series Study station was also analyzed for comparison, and is identical to the reported seawater profile in this region. Applying this improved technique, we are able to generate high-precision and reproducible Nd isotope data for Nd-depleted natural materials, such as seawater, continental runoff, benthic fluxes at continental margins, and marine biogenic carbonate, which can provide pertinent and complementary information about the marine Nd cycle and past ocean circulation. [ABSTRACT FROM AUTHOR]

Near-surface reaction of CO2-bearing fluids with silicate minerals in peridotite and basalt forms solid carbonate minerals. Such processes form abundant veins and travertine deposits, particularly in association with tectonically exposed mantle peridotite. This is important in the global carbon cycle, in weathering, and in understanding physical-chemical interaction during retrograde metamorphism. Enhancing the rate of such reactions is a proposed method for geologic CO2 storage, and perhaps for direct capture of CO2 from near-surface fluids. We review, synthesize, and extend inferences from a variety of sources. We include data from studies on natural peridotite carbonation processes, carbonation kinetics, feedback between permeability and volume change via reaction-driven cracking, and proposed methods for enhancing the rate of natural mineral carbonation via in situ processes (''at the outcrop'') rather than ex situ processes (''at the smokestack''). [ABSTRACT FROM AUTHOR]

Helium is a powerful tracer of primitive material in Earth’s mantle. Extremely high 3He/4He ratios in some ocean-island basalts suggest the presence of relatively undegassed and undifferentiated material preserved in Earth’s mantle. However, terrestrial lavas with high 3He/4He ratios have never been observed to host the primitive lead-isotopic compositions that are required for an early (roughly 4.5 Gyr ago) formation age. Here we show that Cenozoic-era Baffin Island and West Greenland lavas, previously found to host the highest terrestrial-mantle 3He/4He ratios, exhibit primitive lead-isotope ratios that are consistent with an ancient mantle source age of 4.55–4.45?Gyr. The Baffin Island and West Greenland lavas also exhibit 143Nd/144Nd ratios similar to values recently proposed for an early-formed (roughly 4.5 Gyr ago) terrestrial mantle reservoir. The combined helium-, lead- and Nd-isotopic compositions in Baffin Island and West Greenland lavas therefore suggest that their source is the most ancient accessible reservoir in the Earth’s mantle, and it may be parental to all mantle reservoirs that give rise to modern volcanism. [ABSTRACT FROM AUTHOR]

Substantial quantities of terrigenous sediments are known to enter the mantle at subduction zones, but little is known about their fate in the mantle. Subducted sediment may be entrained in buoyantly upwelling plumes and returned to the Earth’s surface at hotspots, but the proportion of recycled sediment in the mantle is small, and clear examples of recycled sediment in hotspot lavas are rare. Here we report remarkably enriched 87Sr/86Sr and 143Nd/144Nd isotope signatures in Samoan lavas from three dredge locations on the underwater flanks of Savai’i island, Western Samoa. The submarine Savai’i lavas represent the most extreme 87Sr/86Sr isotope compositions reported for ocean island basalts to date. The data are consistent with the presence of a recycled sediment component (with a composition similar to the upper continental crust) in the Samoan mantle. Trace-element data show affinities similar to those of the upper continental crust—including exceptionally low Ce/Pb and Nb/U ratios—that complement the enriched 87Sr/86Sr and 143Nd/144Nd isotope signatures. The geochemical evidence from these Samoan lavas significantly redefines the composition of the EM2 (enriched mantle 2; ref. 9) mantle endmember, and points to the presence of an ancient recycled upper continental crust component in the Samoan mantle plume. [ABSTRACT FROM AUTHOR]

Copyright of Geostandards & Geoanalytical Research is the property of Wiley-Blackwell and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Abstract The Dras 1 Volcanic Formation of the Ladakh Himalaya, India, represents the eastern, upper crustal equivalent of the lower crustal gabbros and mantle peridotites of the Kohistan Arc exposed in Pakistan. Together these form a Cretaceous intraoceanic arc now located within the Indus Suture zone between India and Eurasia. During the Late Cretaceous, the Dras–Kohistan Arc, which was located above a north-dipping subduction zone, collided with the south-facing active margin of Eurasia, resulting in a switch from oceanic to continental arc volcanism. In the present study we analyzed samples from the pre-collisional Dras 1 Volcanic Formation and the postcollisional Kardung Volcanic Formation for a suite of trace elements and Nd isotopes. The Kardung Volcanic Formation shows more pronounced light rare earth element enrichment, higher Th/La and lower ℇNd values compared with the Dras 1 Volcanic Formation. These differences are consistent with an increase in the reworking of the continental crust by sediment subduction through the arc after collision. As little as 20% of the Nd in the Dras 1 Volcanic Formation might be provided by sources such as the Karakoram, while approximately 45% of the Nd in the Kardung Volcanic Formation is from this source. However, even before collision, the Dras–Kohistan Arc shows geochemical evidence for more continental sediment contamination than is seen in modern western Pacific arcs, implying its relative proximity to the Eurasian landmass. Comparison of the lava chemistry in the Dras–Kohistan Arc with that in the forearc turbidites suggests that these sediments are partially postcollisional, Jurutze Formation and not all pre-collisional Nindam Formation. Thus, the Dras–Eurasia collision can be dated as Turonian–Santonian (83.5–93.5 Ma), older than it was previously considered to be, but consistent with radiometric ages from Kohistan. [ABSTRACT FROM AUTHOR]

An amendment to this paper has been published and can be accessed via a link at the top of the paper. [ABSTRACT FROM AUTHOR]

Uplift of mountains driven by tectonic forces can influence regional climate as well as regional drainage patterns, which in turn control the discharge of eroded sediment to the ocean. But the nature of the interactions between tectonic forces, climate and drainage evolution remains contested. Here we reconstruct the erosional discharge from the Indus river over the past 30 million years using seismic reflection data obtained from drill core samples from the Arabian Sea and neodymium isotope data. We find that the source of the Indus sediments was dominated by erosion within and north of the Indus suture zone until five million years ago; after that, the river began to receive more erosional products from Himalayan sources. We propose that this change in the erosional pattern is caused by a rerouting of the major rivers of the Punjab into the Indus, which flowed east into the Ganges river before that time. Seismic reflection profiles from the Indus fan suggest high mass accumulation rates during the Pleistocene epoch partly driven by increased drainage to the Indus river after five million years ago and partly by faster erosion linked to a stronger monsoon over the past four million years. Our isotope stratigraphy for the Indus fan provides strong evidence for a significant change in the geometry of western Himalayan river systems in the recent geologic past. [ABSTRACT FROM AUTHOR]